Floating drilling rigs often need riser floatation to maintain safe working conditions. By buoying up the riser, the deck load on the rig can be reduced, and a low center of gravity can be maintained. For this reason, a number of riser floatation devices or riser tensioners, have been proposed. However, those in commercial use have a number of drawbacks.
Slipping conventional riser tensioners is dangerous business, extremely dangerous when on a moving rig in rough weather.
Further, conventional riser tensioners consume large quantities of wire rope, and for that reason have a high operating cost in addition to the high costs of fluid and repair parts used to keep them operational.
Also, conventional riser floatation is expensive, and is bulky to ship. Periodic removal, inspection and reinstallation of conventional floatation is a labor intensive and expensive operation.